Modulator and demodulator

ABSTRACT

A modulator for modulating carrier wave signals with an in-phase component signal and a quadrature component signal includes a fixed frequency signal generating means for generating two fixed-frequency signals differing 90 degrees in phase, a variable frequency signal generating means for generating a signal whose frequency can be varied according to a modulated signal to be produced, an in-phase component carrier wave signal generating means for mixing one fixed-frequency signal and the variable-frequency signal to generate a carrier wave signal for an in-phase component, a quadrature component carrier wave signal generating means for mixing the other fixed-frequency signal and the variable-frequency signal to generate a carrier wave signal for a quadrature component, an in-phase component modulating means for modulating the in-phase component carrier wave signal with the in-phase component signal, and a quadrature component modulating means for modulating the quadrature component carrier wave with the quadrature component signal. A demodulator for demodulating an in-phase component modulated signal and a quadrature component modulated signal includes a fixed frequency signal generating means for generating two fixed-frequency signals differing 90 degrees in phase, a variable frequency signal generating means for generating a signal whose frequency can be varied according to a modulated signal, an in-phase component carrier wave signal generating means for mixing one fixed-frequency signal and the variable-frequency signal to generate a carrier wave signal for an in-phase component, a quadrature component carrier wave signal generating means for mixing the other fixed-frequency signal and the variable-frequency signal to generate a carrier wave signal for a quadrature component, an in-phase component demodulating means for demodulating an in-phase component modulated signal with the in-phase component carrier wave signal to produce an in-phase component signal, and a quadrature component demodulating means for demodulating a quadrature component modulated signal with the quadrature component carrier wave signal to produce a quadrature component signal.

[0001] This application is a Divisional of Ser. No. 10/036,428, filedJan. 7, 2002.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to a modulator for modulating a carrierwave with an in-phase component (I component) signal and a quadraturecomponent (Q component) and a demodulator for demodulating the in-phasecomponent signal and quadrature component signal, particularly to atechnology enabling broadband modulation and demodulation with simplecontrol.

[0004] 2. Description of the Prior Art

[0005] In, for example, intelligent transport systems (ITS) used toincrease traffic efficiency through exchange of information amongpeople, vehicles and roads, consideration is being given to use ofsoftware radio that uses software to send and receive wireless signals.

[0006] Wireless devices such as software radios need to be equipped withmodulator and demodulator units for high-frequency and/or broadbandwireless communication.

[0007] An example configuration of a modulator-demodulator unitconventionally used for analog modulation-demodulation will beexplained.

[0008]FIG. 5 shows the configuration of an analog quadrature modulatorprovided downstream of a digital unit D21. Although the digital unit D21is included in the drawing for convenience of explanation, it should benoted that the digital unit D21 would not ordinarily be a component ofan analog quadrature modulator.

[0009] In the analog quadrature modulator shown in the figure, anin-phase component signal output by the digital unit D21 is input to anin-phase component side mixer (MIX) MI21 and a quadrature componentsignal output by the digital unit D21 is input to a quadrature componentside mixer (MIX) MQ21.

[0010] Further, in this analog quadrature modulator, a local signalgenerator (OSC) OSC11 generates a signal having the frequency of, forinstance, a carrier wave signal ordinarily used in communication(carrier wave frequency) and the signal having this carrier wavefrequency is output as an in-phase component carrier wave signal to thein-phase component side mixer MI21 without modification and the signalhaving the carrier wave frequency is also output to a 90-degree (°)phase shifter P11. The 90-degree phase shifter P11 shifts the signalreceived from the local signal generator OSC11 90 degrees and outputsthe phase-shifted signal to the quadrature component side mixer MQ21 asa quadrature component carrier wave signal.

[0011] The in-phase component side mixer MI21 mixes the in-phasecomponent carrier wave signal received from the local signal generatorOSC11 and the in-phase component signal received from the digital unitD21 to modulate the in-phase component carrier wave signal with thein-phase component signal and outputs the resulting in-phase modulatedcomponent.

[0012] The quadrature component side mixer MQ21 mixes the quadraturecomponent carrier wave signal received from the 90-degree phase shifterP11 and the quadrature component signal received from the digital unitD21 to modulate the quadrature component carrier wave signal with thequadrature component signal and outputs the resulting quadraturemodulated component.

[0013] In this analog quadrature modulator, the in-phase modulatedcomponent output by the in-phase component side mixer MI21 and thequadrature modulated component output by the quadrature component sidemixer MQ21 are synthesized and synthesized signal is output as acomposite signal. The composite signal is a carrier wave frequencysignal including, for example, amplitude information and phaseinformation. By controlling the in-phase component signal and thequadrature component signal output by the digital unit D21 to modify theamplitude information and the phase information, data to be transmittedby frequency modulation, phase modulation and/or amplitude modulationcan be transmitted on the carrier wave. In addition, the compositesignal output by the analog quadrature modulator can be wirelesslytransmitted to another party's wireless device as a wireless signal viaan antenna or the like (not shown).

[0014] The configuration of an analog quadrature demodulator will now beexplained with reference to FIG. 6.

[0015] The analog quadrature demodulator illustrated in the drawing isinput with a carrier wave frequency composite signal including amplitudeinformation or phase information, specifically with a signal transmittedwirelessly from, for example, a wireless device with which communicationis to be conducted and received wirelessly via an antenna (not shown).The received composite signal is divided and input to an in-phasecomponent side mixer MI22 and a quadrature component side mixer MQ22.

[0016] Similarly to the case of the analog quadrature modulator shown inFIG. 5, in this analog quadrature demodulator, a local signal generator(OSC) OSC12 generates a signal of, for instance, a carrier wavefrequency and the signal having this carrier wave frequency is output asan in-phase component carrier wave signal to the in-phase component sidemixer MI22 without modification and the signal having the carrier wavefrequency is also output to a 90-degree phase shifter P12, which shiftsit 90 degrees and outputs the phase-shifted signal to the quadraturecomponent side mixer MQ22 as a quadrature component carrier wave signal.

[0017] The in-phase component side mixer MI22 mixes the in-phasecomponent carrier wave signal received from the local signal generatorOSC12 and the composite signal to demodulate the in-phase modulatedcomponent contained in the composite signal with the in-phase componentcarrier wave signal and outputs the in-phase component signal producedby the demodulation.

[0018] The quadrature component side mixer MQ22 mixes the quadraturecomponent carrier wave signal received from the 90-degree phase shifterP12 and the composite signal to demodulate the quadrature modulatedcomponent contained in composite signal with the quadrature componentcarrier wave signal and outputs the quadrature component signal producedby the demodulation.

[0019] The in-phase component signal and the quadrature component signaloutput by the analog quadrature demodulator are, for example, output toa downstream digital unit (not shown) to acquire receive data based onto the in-phase component signal and the quadrature component signal.

[0020] There will now be explained a configuration for changing thecarrier wave frequency used in modulation and demodulation in the analogquadrature modulator shown in FIG. 5 and the analog quadraturedemodulator shown in FIG. 6.

[0021] Carrier wave frequency change is required, for example, in awireless device or the like that sends and receives wireless signals byswitching among and using carriers of different frequencies spread overa broad band.

[0022] In the analog quadrature modulator shown in FIG. 5 and the analogquadrature demodulator shown in FIG. 6, a configuration enabling carrierwave frequency change can conceivably be implemented, for instance, byinstalling voltage-controlled oscillators (VCOs) in place of the localsignal generators OSC11 and OSC12 and controlling the voltage applied tothe voltage-controlled oscillators to change the frequency of thesignals (local signals) output from the voltage-controlled oscillator tothe in-phase component side mixers MI21, MI22 and the 90-degree phaseshifters P11, P12. With this configuration, however, the fact that thedevices constituting the 90-degree phase shifters P11, P12 havefrequency characteristics would make it possible to achieve accurate90-degree phase shift only in a relatively narrow band, i.e.,frequencies would be present in the required broad band at which a phaseshift greater than 90 degrees or less than 90 degrees arose, makingmodulation-demodulation impossible over a broad band.

[0023] While it is conceivable to overcome this problem by providingmultiple 90-degree phase shifters associated with different frequenciesand using a switch or the like to switch to the one to be used at eachfrequency, this configuration would complicate the control, raise costand increase circuit size, because it would require provision of phaseshifters for the individual frequencies and also increase the number ofcontrol system signals.

[0024] In the modulator taught by JP-A-HEI-5-207080, for example, asynthesizer generates a frequency signal for each channel and, at thetime of shifting the phase of the synthesizer output 90 degrees using avariable 90-degree phase shifter, the variable 90-degree phase shifteris controlled to make the error of a detected quadrature phase zero.However, this configuration requires a circuit for detecting quadraturephase and a circuit for controlling the 90-degree phase shifter to makethe quadrature phase error zero. Control therefore becomes complicatedand, moreover, it is difficult to achieve high accuracy with thevariable phase shifter in a high-frequency band such as thequasi-microwave band.

[0025] In the quadrature phase signal generator circuit taught byJP-A-HEI-10-243037, for example, in order to cause a voltage-controlledoscillator (VCO) to generate a signal whose phase is 90 degreesdifferent from that of a signal output by a local oscillator (localsignal), the voltage-controlled oscillator is controlled based on acomparison of the frequency difference and phase difference of the twosignals. With this configuration, however, when multiple channels areused, for example, the frequency of the signal output by thevoltage-controlled oscillator must be controlled every time thefrequency of the local signal is switched, and phase control of thesignal is also necessary. The control therefore becomes complicated.

[0026] As explained with regard to the prior art, in a conventionalmodulator like that shown in FIG. 5 or demodulator like that shown inFIG. 6, modulation or demodulation over a broad band entails complexcontrol, requires large circuitry and increases cost.

[0027] The present invention was accomplished in light of such problemsof the prior art and has as its object to provide a modulator that whenmodulating a carrier wave with an in-phase component signal and aquadrature component signal can achieve broadband modulation with simplecontrol.

[0028] Another object of the present invention is to provide ademodulator that when demodulating a carrier wave frequency compositesignal into an in-phase component signal and a quadrature componentsignal can achieve broadband demodulation with simple control.

[0029] The modulator and demodulator according to the present inventionenable reduction of circuit size and cost in comparison with the priorart.

SUMMARY OF THE INVENTION

[0030] In order to achieve the foregoing object, the modulator accordingto the invention modulates a carrier wave signal for a carrier wavesignal with an in-phase component signal and modulates a carrier wavesignal for a quadrature component with a quadrature component signal, inthe following manner.

[0031] Specifically, a fixed frequency signal generating means generatestwo signals of fixed frequency differing 90 degrees in phase, a variablefrequency signal generating means generates a signal whose frequency canbe varied according to a modulated signal to be produced, an in-phasecomponent carrier wave signal generating means mixes one signalgenerated by the fixed frequency signal generating means and the signalgenerated by the variable frequency signal generating means to generatea carrier wave signal for an in-phase component, a quadrature componentcarrier wave signal generating means mixes the other signal generated bythe fixed frequency signal generating means and the signal generated bythe variable frequency signal generating means to generate a carrierwave signal for a quadrature component, an in-phase component modulatingmeans modulates the in-phase component carrier wave signal generated bythe in-phase component carrier wave signal generating means with thein-phase component signal and a quadrature component modulating meansmodulates the quadrature component carrier wave signal generated by thequadrature component carrier wave signal generating means with thequadrature component signal.

[0032] Therefore, since two fixed-frequency signals that differ 90degrees in phase are generated, it is easy to ensure that the phasedifference between the two signals is exactly 90 degrees. In addition,since the frequency of the signal generated by the variable frequencysignal generating means according to the frequency of the modulatedsignal to be produced can be controlled and changed so as to change thefrequency of the carrier wave signals for the in-phase component and thequadrature component, broadband modulation can be achieved with simplecontrol.

[0033] The fixed frequency signal generating means can, for example, beconstituted using a digital unit or be constituted using a local signaloscillator and a 90-degree phase shifter.

[0034] In one configuration of the modulator according to the presentinvention, the fixed frequency signal generating means is constitutedusing a local signal oscillator that generates a fixed frequency and a90-degree phase shifter that shifts the phase of the signal generated bythe local signal oscillator 90 degrees. In this case, one or the otherof the signal generated by the local signal oscillator and the signalphase-shifted by the 90-degree phase shifter is mixed by the in-phasecomponent carrier wave signal generating means and the remaining signalis mixed by the quadrature component carrier wave signal generatingmeans.

[0035] As the carrier wave signal for the in-phase component or thequadrature component there is, for example, used a signal having thefrequency of a carrier wave ordinarily used in communication and whenmultiple carrier wave frequencies are used, the multiple carrier wavefrequency signals are switched according to, for example, thecommunication conditions.

[0036] The fixed frequency is not particularly limited and can be set atany of various values based on the use conditions of the modulator.

[0037] The control for changing the frequency of the signal generated bythe variable frequency signal generating means according to thefrequency of the modulated signal to be produced is ordinarily conductedin a mode of matching with the frequency of the carrier wave used forcommunication, i.e. for transmission of the frequency of the generatedin-phase component carrier wave signal or the frequency of the generatedquadrature component carrier wave signal.

[0038] The signal generated by the variable frequency signal generatingmeans is divided into two signals having the same phase, one dividedsignal is mixed by the in-phase component carrier wave signal generatingmeans, and the other divided signal is mixed by the quadrature componentcarrier wave signal generating means.

[0039] When the in-phase component carrier wave signal generating meansor the quadrature component carrier wave signal generating meansgenerates the in-phase component carrier wave signal or the quadraturecomponent carrier wave signal, unnecessary frequency components arepreferably removed from the mixing result of the means by a filter.

[0040] The in-phase component modulating means and the quadraturecomponent modulating means are, for example, constituted as mixers. Forexample, the in-phase component carrier wave signal and the in-phasecomponent signal are mixed to produce an in-phase modulated component,and the quadrature component carrier wave signal and the quadraturecomponent signal are mixed to produce a quadrature modulated component.The in-phase modulated component and the quadrature modulated componentare, for example, synthesized to obtain a composite signal includingamplitude information or phase information.

[0041] Further, the demodulator according to the invention demodulatesan in-phase component modulated signal with an in-phase componentcarrier wave signal to produce an in-phase component signal, anddemodulates a quadrature component modulated signal with a quadraturecomponent carrier wave signal to produce a quadrature component signal,in the following manner.

[0042] Specifically, a fixed frequency signal generating means generatestwo signals of fixed frequency differing 90 degrees in phase, a variablefrequency signal generating means generates a signal whose frequency canbe varied according to a modulated signal, an in-phase component carrierwave signal generating means mixes one signal generated by the fixedfrequency signal generating means and the signal generated by thevariable frequency signal generating means to generate a carrier wavesignal for an in-phase component, a quadrature component carrier wavesignal generating means mixes the other signal generated by the fixedfrequency signal generating means and the signal generated by thevariable frequency signal generating means to generate a carrier wavesignal for a quadrature component, an in-phase component demodulatingmeans demodulates an in-phase component modulated signal with thein-phase component carrier wave signal generated by the in-phasecomponent carrier wave signal generating means to produce an in-phasecomponent signal, and a quadrature component demodulating meansdemodulates a quadrature component modulated signal with the quadraturecomponent carrier wave signal generated by the quadrature componentcarrier wave signal generating means to produce a quadrature componentsignal.

[0043] Therefore, since two fixed-frequency signals that differ 90degrees in phase are generated, it is easy to ensure that the phasedifference between the two signals is exactly 90 degrees. In addition,since the frequency of the signal generated by the variable frequencysignal generating means according to the frequency of the modulatedsignal to be demodulated can be controlled and changed so as to changethe frequency of the carrier wave signals for the in-phase component andthe quadrature component, broadband demodulation can be achieved withsimple control.

[0044] The fixed frequency signal generating means can, for example, beconstituted using a digital unit or be constituted using a local signaloscillator and a 90-degree phase shifter.

[0045] In one configuration of the demodulator according to the presentinvention, the fixed frequency signal generating means is constitutedusing a local signal oscillator that generates a fixed frequency and a90-degree phase shifter that shifts the phase of the signal generated bythe local signal oscillator 90 degrees. In this case, one or the otherof the signals generated by the local signal oscillator and the signalphase-shifted by the 90-degree phase shifter is mixed by the in-phasecomponent carrier wave signal generating means and the remaining signalis mixed by the quadrature component carrier wave signal generatingmeans.

[0046] Although the general practice is for the in-phase componentmodulated signal or the quadrature component modulated signal to beprocessed for demodulation in the form of, for example, a compositesignal synthesizing the two component modulated signals, the twocomponent modulated signals can instead be processed in the form ofseparate signals. In this case, too, the component signal of eachcomponent modulated signal can be demodulated with the correspondingcomponent carrier wave signal.

[0047] As the carrier wave signal for the in-phase component or thequadrature component there is, for example, used a signal having thesame frequency as the in-phase component or quadrature componentmodulated signal to be demodulated and when modulated signals ofmultiple frequencies are demodulated, the carrier wave signals of thesemultiple frequencies are switched according to, for example, thecommunication conditions.

[0048] The fixed frequency is not particularly limited and can be set atany of various values based on the use conditions of the demodulator.

[0049] The control for changing the frequency of the signal generated bythe variable frequency signal generating means according to thefrequency of the demodulated is ordinarily conducted in a mode ofmatching the frequency of the generated in-phase component carrier wavesignal or the frequency of the generated quadrature component carrierwave signal with the frequency of the modulated signal to bedemodulated.

[0050] The signal generated by the variable frequency signal generatingmeans is divided into two signals having the same phase, one dividedsignal is mixed by the in-phase component carrier wave signal generatingmeans, and the other divided signal is mixed by the quadrature componentcarrier wave signal generating means.

[0051] When the in-phase component carrier wave signal generating meansor the quadrature component carrier wave signal generating meansgenerates the in-phase component carrier wave signal or the quadraturecomponent carrier wave signal, unnecessary frequency components arepreferably removed from the mixing result of the means by a filter.

[0052] The in-phase component modulating means and the quadraturecomponent modulating means are, for example, constituted as mixers. Forexample, the in-phase component carrier wave signal and the in-phasecomponent modulated signal are mixed to produce an in-phase componentsignal as an in-phase component demodulation result and the quadraturecomponent carrier wave signal and the quadrature component modulatedsignal are mixed to produce a quadrature component signal as aquadrature component demodulation result, and receive data are acquiredfrom the in-phase component signal and the quadrature component signal.

BRIEF EXPLANATION OF THE DRAWINGS

[0053]FIG. 1 is a diagram showing the configuration of an analogquadrature modulator that is a first embodiment of the presentinvention.

[0054]FIG. 2 is a diagram showing the configuration of an analogquadrature modulator that is a second embodiment of the presentinvention.

[0055]FIG. 3 is a diagram showing the configuration of an analogquadrature demodulator that is a third embodiment of the presentinvention.

[0056]FIG. 4 is a diagram showing the configuration of an analogquadrature demodulator that is a fourth embodiment of the presentinvention.

[0057]FIG. 5 is a diagram showing the configuration of a conventionalanalog quadrature modulator.

[0058]FIG. 6 is a diagram showing the configuration of a conventionalanalog quadrature demodulator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0059] Embodiments of the present invention will now be explained withreference to the drawings.

[0060] A demodulator that is a first embodiment of the invention will beexplained first.

[0061]FIG. 1 shows the configuration of the analog quadrature modulatorof this embodiment provided downstream of a digital unit D1. Althoughthe digital unit D1 is included in the drawing for convenience ofexplanation, it should be noted that the digital unit D1 is notordinarily a component of the analog quadrature modulator.

[0062] The illustrated analog quadrature modulator of this embodimentcomprises a local signal oscillator OSC1 and a 90-degree phase shifterP1 that constitute a processing unit for generating a basic localsignal, a voltage-controlled oscillator VCO1 constituting a processingunit for generating a secondary local signal, an in-phase component sidefirst mixer MI1, filter FI1 and second mixer MI11, and a quadraturecomponent side first mixer MQ1, filter FQ1 and second mixer MQ11. In theanalog quadrature modulator of this embodiment, an in-phase componentsignal output by the digital unit D1 is input to the in-phase componentside second mixer MI11 and a quadrature component signal output by thedigital unit D1 is input to the quadrature component side second mixerMQ11.

[0063] The local signal oscillator OSC1 generates a signal (basic localsignal) f1 whose frequency constitutes a basic carrier wave frequencyand outputs the signal f1 to the 90-degree phase shifter P1 and thein-phase component side first mixer MI1. The basic carrier wavefrequency has a fixed frequency, e.g., has a frequency preset to avoidspurious interference and the like.

[0064] The 90-degree phase shifter P1 shifts the phase of the signal f1received from the local signal oscillator OSC1 90 degrees and outputsthe phase-shifted signal f1′ to the quadrature component side firstmixer MQ1.

[0065] The voltage applied to the voltage-controlled oscillator VCO1 is,for example, controlled by a control unit provided in thevoltage-controlled oscillator VCO1 so as to generate a signal (secondarylocal signal) f2 having a frequency corresponding to the appliedvoltage. The signal f2 is output to the in-phase component side firstmixer MI1 and the quadrature component side first mixer MQ1. Thefrequency of the signal f2 generated by the voltage-controlledoscillator VCO1 is controlled based on the frequency of the modulatedsignal to be generated, i.e., the frequency used for communication(transmission). The functional means for controlling the frequency ofthe voltage-controlled oscillator VCO1 based on the modulated signal tobe generated can, for example, be provided at an arbitrary location inthe communication device equipped with the analog quadrature modulatorof this embodiment.

[0066] One or both of the transmission lines from the voltage-controlledoscillator VCO1 to the in-phase component side first mixer MI1 and thequadrature component side first mixer MQ1 is/are finely adjusted in thelength of the path pattern, for example, so as to set the twotransmission lines to the same phase. In other words, they are set tomake the phase of the signal f2 sent from the voltage-controlledoscillator VCO1 to the in-phase component side first mixer MI1 and thephase of the signal f2 sent from the voltage-controlled oscillator VCO1to the quadrature component side first mixer MQ1 identical.

[0067] The in-phase component side first mixer MI1 mixes the signal f1received from the local signal oscillator OSC1 and the signal f2received from the voltage-controlled oscillator VCO1 and outputs themixing result to the in-phase component side filter FI1. The mixingresult output from the first mixer MI1 to the filter FI1 includes, forexample, a signal having a frequency corresponding to the difference|F1−F2| between the frequency F1 of the signal f1 from the local signaloscillator OSC1 and the frequency F2 of the signal f2 from thevoltage-controlled oscillator VCO1 (difference frequency signal) andsignal having a frequency corresponding to the sum |F1+F2| of thefrequencies F1 and F2 (sum frequency signal). It also includes, forexample, leaked signals from the signals f1, f2 received by the firstmixer MI1 that have frequencies F1, F2 identical with those of thereceived signals f1, f2 (local leak frequency signals).

[0068] The in-phase component side filter FI1 removes unnecessaryfrequency components from the mixing result received from the in-phasecomponent side first mixer MI1 by filtering and outputs the filteredsignal fLO to the in-phase component side second mixer MI11 as anin-phase component carrier wave signal. In this embodiment, one or theother of the aforesaid difference frequency signal and sum frequencysignal is output to the second mixer MI11 as the in-phase componentcarrier wave signal fLO removed of unnecessary frequency components. Onthe other hand, the remaining one of the difference frequency signal andthe sum frequency signal (the image frequency signal component) isremoved as an unnecessary frequency component by the filter FI1 and thecharacteristics of the filter FI1 are set so that the local leakfrequency signals are also removed by the filter FI1.

[0069] An ordinary band-pass filter or any of various other filters canbe used for the filter FI1. When the image frequency is high, forexample, a low-pass filter can be used, and when the image frequency islow, a high-pass filter can be used.

[0070] The in-phase component side second mixer MI11 mixes the in-phasecomponent carrier wave signal fLO received from the in-phase componentside filter FI1 and an in-phase component signal received from thedigital unit D1 and outputs the result of modulating the in-phasecomponent carrier wave signal with the in-phase component signal as anin-phase modulated component.

[0071] The quadrature component side first mixer MQ1, filter FQ1 andsecond mixer MQ11 conduct processing similar to that conducted by thein-phase component side first mixer MI1, filter FI1 and second mixerMI11.

[0072] Specifically, the quadrature component side first mixer MQ1 mixesthe signal f1′ received from the 90-degree phase shifter P1 and thesignal f2 received from the voltage-controlled oscillator VCO1 andoutputs the mixing result to the quadrature component side filter FQ1.

[0073] The quadrature component side filter FQ1, which may have the samefrequency characteristics as the in-phase component side filter FI1,removes unnecessary frequency components from the mixing result receivedfrom the quadrature component side first mixer MQ1 by filtering andoutputs the filtered signal fLO′ to the quadrature component side secondmixer MQ11 as a quadrature component carrier wave signal. As thequadrature component carrier wave signal there is used, for example, asignal that has the same frequency and amplitude as the in-phasecomponent carrier wave signal but whose phase is shifted 90 degreesrelative thereto.

[0074] The quadrature component side second mixer MQ11 mixes thequadrature component carrier wave signal fLO′ received from thequadrature component side filter FQ1 and a quadrature component signalreceived from the digital unit D1 and outputs the result of modulatingthe quadrature component carrier wave signal with the quadraturecomponent signal as a quadrature modulated component.

[0075] The in-phase modulated component output by the in-phase componentside second mixer MI11 and the quadrature modulated component output bythe quadrature component side second mixer MQ11 are then synthesized bya synthesizer (not shown), for example, and the synthesis result isoutput as a composite signal. The composite signal output by the analogquadrature modulator of this embodiment is wirelessly transmitted froman antenna (not shown) to, for instance, the wireless device of anotherparty with which communication is to be conducted. The frequency of thecomposite signal output by the analog quadrature modulator of thisembodiment is changed according to the communication conditions and thelike by controlling the voltage-controlled oscillator VCO1 to vary thefrequency thereof. This enables modulation over a broad band.

[0076] The analog quadrature modulator according to this embodiment canthus conduct modulation over a broad frequency range by simple controleven when incorporated in a wireless device or the like thattransmits/receives signals over a broad band, without increasing thenumber of control system signals, cost or circuit size. Since thefrequency of the signal f1 whose phase is shifted by the 90-degree phaseshifter P1 is fixed, moreover, the accuracy of the 90-degree phase shiftby the 90-degree phase shifter P1 can be ensured. The analog quadraturemodulator according this embodiment can, for example, control themodulation processing over a broad band merely by conventional frequencycontrol, e.g., by controlling the frequency of the voltage-controlledoscillator VCO1 according to the frequency of the composite signal to begenerated.

[0077] In this embodiment, the local signal oscillator OSC1 and the90-degree phase shifter P1 constitute the fixed frequency signalgenerating means, the voltage-controlled oscillator VCO1 constitutes thevariable frequency signal generating means, the in-phase component sidefirst mixer MI1 and filter FI1 constitute the in-phase component carrierwave signal generating means, the quadrature component side first mixerMQ1 and filter FQ1 constitute the quadrature component carrier wavesignal generating means, the in-phase component side second mixer MI11constitutes the in-phase component modulating means, and the quadraturecomponent side second mixer MQ11 constitutes the quadrature componentmodulating means.

[0078] A modulator that is a second embodiment of the invention will nowbe explained.

[0079]FIG. 2 shows the configuration of the analog quadrature modulatorof this embodiment provided downstream of a digital unit D2. Althoughthe digital unit D2 is included in the drawing for convenience ofexplanation, it should be noted that the digital unit D2 is notordinarily a component of the analog quadrature modulator.

[0080] The illustrated analog quadrature modulator of this embodimentcomprises a digital unit D11 constituting a processing unit forgenerating a basic local signal, a voltage-controlled oscillator VCO2constituting a processing unit for generating a secondary local signal,an in-phase component side first mixer MI2, filter FI2 and second mixerMI12, and a quadrature component side first mixer MQ2, filter FQ2 andsecond mixer MQ12. In the analog quadrature modulator of thisembodiment, an in-phase component signal output by the digital unit D2is input to the in-phase component side second mixer MI12 and aquadrature component signal output by the digital unit D2 is input tothe quadrature component side second mixer MQ12.

[0081] The configuration and operation of the analog quadraturemodulator of this embodiment are the same as the configuration andoperation of the analog quadrature modulator according to the firstembodiment shown in FIG. 1, except for the point that the digital unitD11 generates the basic carrier wave frequency signal f1 and outputs thesignal f1 to the in-phase component side first mixer MI2 and the pointthat the digital unit D11 generates the signal f1′ equivalent to asignal obtained by shifting the phase of the signal f1 90 degrees andoutputs the signal f1′ to the quadrature component side first mixer MQ2,i.e., except for the configuration for generating the basic localsignal.

[0082] In this embodiment, since the frequencies of the basic localsignals f1, f1′ input to the in-phase component side first mixer MI2 andthe quadrature component side first mixer MQ2 are fixed, when thefrequency is a relatively low one of, for example, 100 MHz or lower, itis easily possible, in consideration of spurious interference and thelike, to have the digital unit D11 output the basic local signal f1 forthe in-phase component and the basic local signal f1′ for the quadraturecomponent as digital signals.

[0083] Thus the analog quadrature modulator according to this embodimentcan, as was explained earlier regarding the analog quadrature modulatoraccording to the first embodiment, also conduct modulation over a wideband with simple control.

[0084] In this embodiment, the digital unit D11 constitutes the fixedfrequency signal generating means.

[0085] A demodulator that is a third embodiment of the present inventionwill now be explained.

[0086]FIG. 3 shows the configuration of the analog quadraturedemodulator of this embodiment.

[0087] The illustrated analog quadrature demodulator of this embodimentcomprises a local signal oscillator OSC2 and a 90-degree phase shifterP2 that constitute a processing unit for generating a basic localsignal, a voltage-controlled oscillator VCO3 constituting a processingunit for generating a secondary local signal, an in-phase component sidefirst mixer MI3, filter FI3 and second mixer MI13, and a quadraturecomponent side first mixer MQ3, filter FQ3 and second mixer MQ13. Theanalog quadrature demodulator of this embodiment is input with acomposite signal transmitted wirelessly from, for example, a wirelessdevice with which communication is to be conducted and receivedwirelessly via an antenna (not shown). The composite signal is dividedby a distributor (not shown), for example. One divided signal is inputto the in-phase component side second mixer MI13 and the other dividedsignal is input to the quadrature component side second mixer MQ13.

[0088] The local signal oscillator OSC2 generates a signal (basic localsignal) f1 whose frequency constitutes a basic carrier wave frequencyand outputs the signal f1 to the 90-degree phase shifter P2 and thein-phase component side first mixer MI3. The basic carrier wavefrequency has a fixed frequency, e.g., has a frequency preset to avoidspurious interference and the like.

[0089] The 90-degree phase shifter P2 shifts the phase of the signal f1received from the local signal oscillator OSC2 90 degrees and outputsthe phase-shifted signal f1′ to the quadrature component side firstmixer MQ3.

[0090] The voltage applied to the voltage-controlled oscillator VCO3 is,for example, controlled by a control unit provided in thevoltage-controlled oscillator VCO3 so as to generate a signal (secondarylocal signal) f2 having a frequency corresponding to the appliedvoltage. The signal f2 is output to the in-phase component side firstmixer MI3 and the quadrature component side first mixer MQ3. Thefrequency of the signal f2 generated by the voltage-controlledoscillator VCO3 is controlled based on the frequency of the inputcomposite signal, i.e., the frequency of the signal to be received. Thefunctional means for controlling the frequency of the voltage-controlledoscillator VCO3 based on the composite signal can, for example, beprovided at an arbitrary location in the communication device equippedwith the analog quadrature demodulator of this embodiment.

[0091] One or both of the transmission lines from the voltage-controlledoscillator VCO3 to the in-phase component side first mixer MI3 and thequadrature component side first mixer MQ3 is/are finely adjusted in thelength of the path pattern, for example, so as to set the twotransmission lines to the same phase. In other words, they are set tomake the phase of the signal f2 sent from the voltage-controlledoscillator VCO3 to the in-phase component side first mixer MI3 and thephase of the signal f2 sent from the voltage-controlled oscillator VCO3to the quadrature component side first mixer MQ3 identical.

[0092] The in-phase component side first mixer MI3 mixes the signal f1received from the local signal oscillator OSC2 and the signal f2received from the voltage-controlled oscillator VCO3 and outputs themixing result to the in-phase component side filter FI3. The mixingresult output from the first mixer MI3 to the filter FI3 includes, forexample, a signal having a frequency corresponding to the difference|F1−F2| between the frequency F1 of the signal f1 from the local signaloscillator OSC2 and the frequency F2 of the signal f2 from thevoltage-controlled oscillator VCO3 (difference frequency signal) andsignal having a frequency corresponding to the sum |F1+F2| of thefrequencies F1 and F2 (sum frequency signal). It also includes, forexample, leaked signals from the signals f1, f2 received by the firstmixer MI3 that have frequencies F1, F2 identical with those of thereceived signals f1, f2 (local leak frequency signals).

[0093] The in-phase component side filter FI3 removes unnecessaryfrequency components from the mixing result received from the in-phasecomponent side first mixer MI3 by filtering and outputs the filteredsignal fLO to the in-phase component side second mixer MI13 as anin-phase component carrier wave signal. In this embodiment, one or theother of the aforesaid difference frequency signal and sum frequencysignal is output to the second mixer MI13 as the in-phase componentcarrier wave signal fLO removed of unnecessary frequency components. Onthe other hand, the remaining one of the difference frequency signal andthe sum frequency signal (the image frequency signal component) isremoved as an unnecessary frequency component by the filter FI3 and thecharacteristics of the filter FI3 are set so that the local leakfrequency signals are also removed by the filter FI3.

[0094] An ordinary band-pass filter or any of various other filters canbe used for the filter FI3. When the image frequency is high, forexample, a low-pass filter can be used, and when the image frequency islow, a high-pass filter can be used.

[0095] The in-phase component side second mixer MI13 mixes the in-phasecomponent carrier wave signal fLO received from the in-phase componentside filter FI3 and the composite signal to demodulate the compositesignal with the in-phase component carrier wave signal fLO and outputsthe in-phase component signal produced by the demodulation.

[0096] The quadrature component side first mixer MQ3, filter FQ3 andsecond mixer MQ13 conduct processing similar to that conducted by thein-phase component side first mixer MI3, filter FI3 and second mixerMI13.

[0097] Specifically, the quadrature component side first mixer MQ3 mixesthe signal f1′ received from the 90-degree phase shifter P2 and thesignal f2 received from the voltage-controlled oscillator VCO3 andoutputs the mixing result to the quadrature component side filter FQ3.

[0098] The quadrature component side filter FQ3, which may have the samefrequency characteristics as the in-phase component side filter FI3,removes unnecessary frequency components from the mixing result receivedfrom the quadrature component side first mixer MQ3 by filtering andoutputs the filtered signal fLO′ to the quadrature component side secondmixer MQ13 as a quadrature component carrier wave signal. As thequadrature component carrier wave signal there is used, for example, asignal that has the same frequency and amplitude as the in-phasecomponent carrier wave signal but whose phase is shifted 90 degreesrelative thereto.

[0099] The quadrature component side second mixer MQ13 mixes thequadrature component carrier wave signal fLO′ received from thequadrature component side filter FQ3 and the composite signal todemodulate the composite signal with the quadrature component carrierwave signal fLO′ and outputs the quadrature component signal produced bythe demodulation.

[0100] The in-phase component signal output by the in-phase componentside second mixer MI13 and the quadrature component signal output by thequadrature component side second mixer MQ13 are then sent to, forexample, a digital unit (not shown) provided downstream of analogquadrature demodulator of this embodiment to acquire receive data fromthe in-phase component signal and the quadrature component signal. Whenthe frequency of the composite signal input to the analog quadraturedemodulator of this embodiment varies, demodulation can be conductedover a broad band in response to the frequency variation of thecomposite signal by controlling the voltage-controlled oscillator VCO3to vary its frequency according to the frequency of the compositesignal.

[0101] The analog quadrature demodulator according to this embodimentcan thus conduct demodulation over a broad frequency range by simplecontrol even when incorporated in a wireless device or the like thattransmits/receives signals over a broad band, without increasing thenumber of control system signals, cost or circuit size. Since thefrequency of the signal f1 whose phase is shifted by the 90-degree phaseshifter P2 is fixed, moreover, the accuracy of the 90-degree phase shiftby the 90-degree phase shifter P2 can be ensured. The analog quadraturedemodulator according this embodiment can, for example, control thedemodulation processing over a broad band merely by conventionalfrequency control, e.g., by controlling the frequency of thevoltage-controlled oscillator VCO3 according to the frequency of thecomposite signal.

[0102] In this embodiment, the local signal oscillator OSC2 and the90-degree phase shifter P2 constitute the fixed frequency signalgenerating means, the voltage-controlled oscillator VCO3 constitutes thevariable frequency signal generating means, the in-phase component sidefirst mixer MI3 and filter FI3 constitute the in-phase component carrierwave signal generating means, the quadrature component side first mixerMQ3 and filter FQ3 constitute the quadrature component carrier wavesignal generating means, the in-phase component side second mixer MI13constitutes the in-phase component demodulating means, and thequadrature component side second mixer MQ13 constitutes the quadraturecomponent demodulating means. In this embodiment, the in-phase componentmodulated signal (in-phase modulated component) and the quadraturecomponent modulated signal (quadrature modulated component) areprocessed in the form of a synthesized composite signal.

[0103] A demodulator that is a fourth embodiment of the presentinvention will now be explained.

[0104]FIG. 4 shows the configuration of the analog quadraturedemodulator of this embodiment.

[0105] The illustrated analog quadrature demodulator of this embodimentcomprises a digital unit D12 constituting a processing unit forgenerating a basic local signal, a voltage-controlled oscillator VCO4constituting a processing unit for generating a secondary local signal,an in-phase component side first mixer MI4, filter FI4 and second mixerMI14, and a quadrature component side first mixer MQ4, filter FQ4 andsecond mixer MQ14. The analog quadrature demodulator of this embodimentis input with a composite signal transmitted wirelessly from, forexample, a wireless device with which communication is to be conductedand received wirelessly via an antenna (not shown). The composite signalis divided by a distributor (not shown), for example. One divided signalis input to the in-phase component side second mixer MI14 and the otherdivided signal is input to the quadrature component side second mixerMQ14.

[0106] The configuration and operation of the analog quadraturedemodulator of this embodiment are the same as the configuration andoperation of the analog quadrature demodulator according to the thirdembodiment shown in FIG. 3, except for the point that the digital unitD12 generates the basic carrier wave frequency signal f1 and outputs thesignal f1 to the in-phase component side first mixer MI4 and the pointthat the digital unit D12 generates the signal f1′ equivalent to asignal obtained by shifting the phase of the signal f1 90 degrees andoutputs the signal f1′ to the quadrature component side first mixer MQ4,i.e., except for the configuration for generating the basic localsignal.

[0107] In this embodiment, since the frequencies of the basic localsignals f1, f1′ input to the in-phase component side first mixer MI4 andthe quadrature component side first mixer MQ4 are fixed, when thefrequency is a relatively low one of, for example, 100 MHz or lower, itis easily possible, in consideration of spurious interference and thelike, to have the digital unit D12 output the basic local signal f1 forthe in-phase component and the basic local signal f1′ for the quadraturecomponent as digital signals.

[0108] Thus the analog quadrature demodulator according to thisembodiment can, as was explained earlier regarding the analog quadraturedemodulator according to the third embodiment, also conduct demodulationover a wide band with simple control.

[0109] In this embodiment, the digital unit D12 constitutes the fixedfrequency signal generating means.

[0110] The configurations of the modulator and demodulator according tothis invention are not limited to those set out in the foregoing and anyof various other configurations can be adopted instead.

[0111] In addition, the field of application of the invention is notlimited to that discussed in the foregoing and application in variousother fields is also possible.

[0112] The modulator and demodulator of this invention are suitable forapplication in, for example, in the wireless communication devices ofmobile communication systems such the wireless communication devices ofan intelligent transport system, a mobile phone system and a PersonalHandy phone System (PHS). However, they can also be applied in thecommunication equipment of various other kinds of systems. Moreover,application is not limited to wireless communication and application towire communication is also possible.

[0113] In addition, the various types of processing performed in themodulator and demodulator according to this invention may be constitutedby being implemented in hardware resources equipped with a processor andmemory and the like, for example, being controlled by means of aprocessor executing a control program stored in ROM (Read Only Memory).Further, the various functional means for executing this processing mayalso be constituted as independent physical circuits.

[0114] In addition, the present invention may also be understood as theaforesaid program itself or as a Floppy Disk®, CD (compact disk)-ROM orother computer-readable recording media in which the program is stored,so that the processing according to the present invention can beimplemented by loading said control program from the recording mediuminto a computer and executing the program by a processor.

[0115] As explained in the foregoing, the modulator according to thepresent invention is adapted such that, when modulating an in-phasecomponent carrier wave signal with an in-phase component signal andmodulating a quadrature component carrier wave signal with a quadraturecomponent signal, it generates two basic local signals of fixedfrequency differing 90 degrees in phase, generates a secondary localsignal whose frequency can be varied according to a modulated signal tobe produced, mixes one basic local signal and the secondary local signalto generate a carrier wave signal for an in-phase component, mixes theother basic local signal and the secondary local signal to generate acarrier wave signal for a quadrature component, modulates the generatedin-phase component carrier wave signal with the in-phase componentsignal and modulates the generated quadrature component carrier wavesignal with the quadrature component signal. Broadband modulation cantherefore be achieved with simple control.

[0116] The demodulator according to the present invention is adaptedsuch that, when demodulating an in-phase component modulated signal withan in-phase component carrier wave signal to produce an in-phasecomponent signal and demodulating a quadrature component modulatedsignal with a quadrature component carrier wave signal to produce aquadrature component signal, it generates two basic local signals offixed frequency differing 90 degrees in phase, generates a secondarylocal signal whose frequency can be varied according to a modulatedsignal, mixes one basic local signal and the secondary local signal togenerate a carrier wave signal for an in-phase component, mixes theother basic local signal and the secondary local signal to generate acarrier wave signal for a quadrature component, demodulates an in-phasecomponent modulated signal with the generated in-phase component carrierwave signal to produce an in-phase component signal, and demodulates aquadrature component modulated signal with the generated quadraturecomponent carrier wave signal to produce a quadrature component signal.Broadband demodulation can therefore be achieved with simple control.

What is claimed is:
 1. A demodulator for demodulating an in-phasecomponent modulated signal with an in-phase component carrier wavesignal to produce an in-phase component signal and demodulating aquadrature component modulated signal with a quadrature componentcarrier wave signal to produce a quadrature component signal, thedemodulator comprising: fixed frequency signal generating means forgenerating two signals of fixed frequency differing 90 degrees in phase;variable frequency signal generating means for generating a signal whosefrequency can be varied according to a modulated signal; in-phasecomponent carrier wave signal generating means for mixing one signalgenerated by the fixed frequency signal generating means and the signalgenerated by the variable frequency signal generating means to generatea carrier wave signal for an in-phase component; quadrature componentcarrier wave signal generating means for mixing the other signalgenerated by the fixed frequency signal generating means and the signalgenerated by the variable frequency signal generating means to generatea carrier wave signal for a quadrature component; in-phase componentdemodulating means for demodulating an in-phase component modulatedsignal with the in-phase component carrier wave signal generated by thein-phase component carrier wave signal generating means to produce anin-phase component signal; and quadrature component demodulating meansfor demodulating a quadrature component modulated signal with thequadrature component carrier wave signal generated by the quadraturecomponent carrier wave signal generating means to produce a quadraturecomponent signal.
 2. A demodulator according to claim 1, wherein: thefixed frequency signal generating means is constituted using a localsignal oscillator that generates a fixed frequency and a 90-degree phaseshifter that shifts the phase of the signal generated by the localsignal oscillator 90 degrees.
 3. A demodulator according to claim 2,wherein: the variable frequency signal generating means is constitutedby a voltage-controlled oscillator, the in-phase component carrier wavesignal generating means is constituted by an in-phase component sidefirst mixer and filter, the quadrature component carrier wave signalgenerating means is constituted by a quadrature component side firstmixer and filter, the in-phase component demodulating means isconstituted by an in-phase component side second mixer, and thequadrature component demodulating means is constituted by a quadraturecomponent side second mixer; the local signal oscillator generates asignal whose frequency constitutes a basic carrier wave frequency andoutputs the signal to the 90-degree phase shifter and the in-phasecomponent side first mixer; the 90-degree phase shifter shifts the phaseof the signal received from the local signal oscillator 90 degrees andoutputs the phase-shifted signal to the quadrature component side firstmixer; the voltage-controlled oscillator generates a signal having afrequency corresponding to a voltage applied thereto and outputs thesignal to the in-phase component side first mixer and the quadraturecomponent side first mixer; the in-phase component side first mixermixes the signal received from the local signal oscillator and thesignal received from the voltage-controlled oscillator and outputs themixing result to the in-phase component side filter; the in-phasecomponent side filter removes unnecessary frequency components from themixing result received from the in-phase component side first mixer byfiltering and outputs the filtered signal to the in-phase component sidesecond mixer as an in-phase component carrier wave signal; the in-phasecomponent side second mixer mixes the in-phase component carrier wavesignal received from the in-phase component side filter and thecomposite signal to demodulate the composite signal with the in-phasecomponent carrier wave signal and outputs the in-phase component signalproduced by the demodulation; the quadrature component side first mixermixes the signal received from the 90-degree phase shifter and thesignal received from the voltage-controlled oscillator and outputs themixing result to the quadrature component side filter; the quadraturecomponent side filter removes unnecessary frequency components from themixing result received from the quadrature component side first mixer byfiltering and outputs the filtered signal to the quadrature componentside second mixer as a quadrature component carrier wave signal; and thequadrature component side second mixer mixes the quadrature componentcarrier wave signal received from the quadrature component side filterand the composite signal to demodulate the composite signal with thequadrature component carrier wave signal and outputs the quadraturecomponent signal produced by the demodulation.
 4. A demodulatoraccording to claim 1, wherein: the fixed frequency signal generatingmeans is constituted by a digital unit, the variable frequency signalgenerating means is constituted by a voltage-controlled oscillator, thein-phase component carrier wave signal generating means is constitutedby an in-phase component side first mixer and filter, the quadraturecomponent carrier wave signal generating means is constituted by aquadrature component side first mixer and filter, the in-phase componentdemodulating means is constituted by an in-phase component side secondmixer, and the quadrature component demodulating means is constituted bya quadrature component side second mixer; the digital unit generates abasic carrier wave frequency signal and outputs the signal to thein-phase component side first mixer and generates a signal equivalent toa signal obtained by shifting the phase of the basic carrier wavefrequency signal 90 degrees and outputs the signal to the quadraturecomponent side first mixer; the voltage-controlled oscillator generatesa signal having a frequency corresponding to a voltage applied theretoand outputs the signal to the in-phase component side first mixer andthe quadrature component side first mixer; the in-phase component sidefirst mixer mixes the signal received from the digital unit and thesignal received from the voltage-controlled oscillator and outputs themixing result to the in-phase component side filter; the in-phasecomponent side filter removes unnecessary frequency components from themixing result received from the in-phase component side first mixer byfiltering and outputs the filtered signal to the in-phase component sidesecond mixer as an in-phase component carrier wave signal; the in-phasecomponent side second mixer mixes the in-phase component carrier wavesignal received from the in-phase component side filter and thecomposite signal to demodulate the composite signal with the in-phasecomponent carrier wave signal and outputs the in-phase component signalproduced by the demodulation; the quadrature component side first mixermixes the signal received from the digital unit and the signal receivedfrom the voltage-controlled oscillator and outputs the mixing result tothe quadrature component side filter; the quadrature component sidefilter removes unnecessary frequency components from the mixing resultreceived from the quadrature component side first mixer by filtering andoutputs the filtered signal to the quadrature component side secondmixer as a quadrature component carrier wave signal; and the quadraturecomponent side second mixer mixes the quadrature component carrier wavesignal received from the quadrature component side filter and thecomposite signal to demodulate the composite signal with the quadraturecomponent carrier wave signal and outputs the quadrature componentsignal produced by the demodulation.
 5. A communication device equippedwith a demodulator for demodulating an in-phase component modulatedsignal with an in-phase component carrier wave signal to produce anin-phase component signal and demodulating a quadrature componentmodulated signal with a quadrature component carrier wave signal toproduce a quadrature component signal and adapted to conductcommunication using carrier waves of multiple frequencies and demodulatereceived modulated signals with the demodulator, the demodulator of thecommunication device comprising fixed frequency signal generating meansfor generating two signals of fixed frequency differing 90 degrees inphase; variable frequency signal generating means for generating asignal whose frequency can be varied according to a modulated signal;in-phase component carrier wave signal generating means for mixing onesignal generated by the fixed frequency signal generating means and thesignal generated by the variable frequency signal generating means togenerate a carrier wave signal for an in-phase component; quadraturecomponent carrier wave signal generating means for mixing the othersignal generated by the fixed frequency signal generating means and thesignal generated by the variable frequency signal generating means togenerate a carrier wave signal for a quadrature component; in-phasecomponent demodulating means for demodulating an in-phase componentmodulated signal with the in-phase component carrier wave signalgenerated by the in-phase component carrier wave signal generating meansto produce an in-phase component signal; and quadrature componentdemodulating means for demodulating a quadrature component modulatedsignal with the quadrature component carrier wave signal generated bythe quadrature component carrier wave signal generating means to producea quadrature component signal.
 6. A communication device according toclaim 5, wherein: the fixed frequency signal generating means isconstituted using a local signal oscillator that generates a fixedfrequency and a 90-degree phase shifter that shifts the phase of thesignal generated by the local signal oscillator 90 degrees.
 7. Acommunication device according to claim 6, wherein: the variablefrequency signal generating means is constituted by a voltage-controlledoscillator, the in-phase component carrier wave signal generating meansis constituted by an in-phase component side first mixer and filter, thequadrature component carrier wave signal generating means is constitutedby a quadrature component side first mixer and filter, the in-phasecomponent demodulating means is constituted by an in-phase componentside second mixer, and the quadrature component demodulating means isconstituted by a quadrature component side second mixer; the localsignal oscillator generates a signal whose frequency constitutes a basiccarrier wave frequency and outputs the signal to the 90-degree phaseshifter and the in-phase component side first mixer; the 90-degree phaseshifter shifts the phase of the signal received from the local signaloscillator 90 degrees and outputs the phase-shifted signal to thequadrature component side first mixer; the voltage-controlled oscillatorgenerates a signal having a frequency corresponding to a voltage appliedthereto and outputs the signal to the in-phase component side firstmixer and the quadrature component side first mixer; the in-phasecomponent side first mixer mixes the signal received from the localsignal oscillator and the signal received from the voltage-controlledoscillator and outputs the mixing result to the in-phase component sidefilter; the in-phase component side filter removes unnecessary frequencycomponents from the mixing result received from the in-phase componentside first mixer by filtering and outputs the filtered signal to thein-phase component side second mixer as an in-phase component carrierwave signal; the in-phase component side second mixer mixes the in-phasecomponent carrier wave signal received from the in-phase component sidefilter and the composite signal to demodulate the composite signal withthe in-phase component carrier wave signal and outputs the in-phasecomponent signal produced by the demodulation; the quadrature componentside first mixer mixes the signal received from the 90-degree phaseshifter and the signal received from the voltage-controlled oscillatorand outputs the mixing result to the quadrature component side filter;the quadrature component side filter removes unnecessary frequencycomponents from the mixing result received from the quadrature componentside first mixer by filtering and outputs the filtered signal to thequadrature component side second mixer as a quadrature component carrierwave signal; and the quadrature component side second mixer mixes thequadrature component carrier wave signal received from the quadraturecomponent side filter and the composite signal to demodulate thecomposite signal with the quadrature component carrier wave signal andoutputs the quadrature component signal produced by the demodulation. 8.A communication device according to claim 5, wherein: the fixedfrequency signal generating means is constituted by a digital unit, thevariable frequency signal generating means is constituted by avoltage-controlled oscillator, the in-phase component carrier wavesignal generating means is constituted by an in-phase component sidefirst mixer and filter, the quadrature component carrier wave signalgenerating means is constituted by a quadrature component side firstmixer and filter, the in-phase component demodulating means isconstituted by an in-phase component side second mixer, and thequadrature component demodulating means is constituted by a quadraturecomponent side second mixer; the digital unit generates a basic carrierwave frequency signal and outputs the signal to the in-phase componentside first mixer and generates a signal equivalent to a signal obtainedby shifting the phase of the basic carrier wave frequency signal 90degrees and outputs the signal to the quadrature component side firstmixer; the voltage-controlled oscillator generates a signal having afrequency corresponding to a voltage applied thereto and outputs thesignal to the in-phase component side first mixer and the quadraturecomponent side first mixer; the in-phase component side first mixermixes the signal received from the digital unit and the signal receivedfrom the voltage-controlled oscillator and outputs the mixing result tothe in-phase component side filter; the in-phase component side filterremoves unnecessary frequency components from the mixing result receivedfrom the in-phase component side first mixer by filtering and outputsthe filtered signal to the in-phase component side second mixer as anin-phase component carrier wave signal; the in-phase component sidesecond mixer mixes the in-phase component carrier wave signal receivedfrom the in-phase component side filter and the composite signal todemodulate the composite signal with the in-phase component carrier wavesignal and outputs the in-phase component signal produced by thedemodulation; the quadrature component side first mixer mixes the signalreceived from the digital unit and the signal received from thevoltage-controlled oscillator and outputs the mixing result to thequadrature component side filter; the quadrature component side filterremoves unnecessary frequency components from the mixing result receivedfrom the quadrature component side first mixer by filtering and outputsthe filtered signal to the quadrature component side second mixer as aquadrature component carrier wave signal; and the quadrature componentside second mixer mixes the quadrature component carrier wave signalreceived from the quadrature component side filter and the compositesignal to demodulate the composite signal with the quadrature componentcarrier wave signal and outputs the quadrature component signal producedby the demodulation.